Photosensitive imaging devices and associated methods

ABSTRACT

Backside illuminated photosensitive devices and associated methods are provided. In one aspect, for example, a backside-illuminated photosensitive imager device can include a semiconductor substrate having multiple doped regions forming a least one junction, a textured region coupled to the semiconductor substrate and positioned to interact with electromagnetic radiation, and a passivation region positioned between the textured region and the at least one junction. The passivation region is positioned to isolate the at least one junction from the textured region, and the semiconductor substrate and the textured region are positioned such that incoming electromagnetic radiation passes through the semiconductor substrate before contacting the textured region. Additionally, the device includes an electrical transfer element coupled to the semiconductor substrate to transfer an electrical signal from the at least one junction.

PRIORITY DATA

This application is a continuation of U.S. patent application Ser. No.13/050,557, filed on Mar. 17, 2011, which is a continuation-in-part ofU.S. patent application Ser. No. 12/885,158, filed on Sep. 17, 2010,which claims the benefit of U.S. Provisional Patent Application Ser. No.61/243,434, filed on Sep. 17, 2009, U.S. Provisional Patent ApplicationSer. No. 61/311,004 filed on Mar. 5, 2010, and U.S. Provisional PatentApplication Ser. No. 61/311,107, filed on Mar. 5, 2010, each of which isincorporated herein by reference. U.S. patent application Ser. No.13/050,557 also claims the benefit of U.S. Provisional Application Ser.No. 61/443,988, filed on Feb. 17, 2011, which is incorporated herein byreference.

BACKGROUND

The interaction of light with semiconductor materials has been asignificant innovation. Silicon imaging devices are used in varioustechnologies, such as digital cameras, optical mice, video cameras, cellphones, and the like. Charge-coupled devices (CCDs) were widely used indigital imaging, and were later improved upon by complementarymetal-oxide-semiconductor (CMOS) imagers having improved performance.Many traditional CMOS imagers utilize front side illumination (FSI). Insuch cases, electromagnetic radiation is incident upon the semiconductorsurface containing the CMOS devices and circuits. Backside illuminationCMOS imagers have also been used, and in many designs electromagneticradiation is incident on the semiconductor surface opposite the CMOSdevices and circuits. CMOS sensors are typically manufactured fromsilicon and can covert visible incident light into a photocurrent andultimately into a digital image. Silicon-based technologies fordetecting infrared incident electromagnetic radiation have beenproblematic, however, because silicon is an indirect bandgapsemiconductor having a bandgap of about 1.1 eV. Thus the absorption ofelectromagnetic radiation having wavelengths of greater than about 1100nm is, therefore, very low in silicon.

SUMMARY

The present disclosure provides backside-illuminated photosensitiveimager devices and associated methods. In one aspect, for example, abackside-illuminated photosensitive imager device can include asemiconductor substrate having multiple doped regions forming a leastone junction, a textured region coupled to the semiconductor substrateand positioned to interact with electromagnetic radiation, and apassivation region positioned between the textured region and the atleast one junction. The passivation region is positioned to isolate theat least one junction from the textured region, and the semiconductorsubstrate and the textured region are positioned such that incomingelectromagnetic radiation passes through the semiconductor substratebefore contacting the textured region. Additionally, the device includesan electrical transfer element coupled to the semiconductor substrate totransfer an electrical signal from the at least one junction. In someaspects, the passivation region is positioned to physically isolate thetextured region from the at least one junction. In other aspects, thepassivation region is positioned to electrically isolate the texturedregion from the at least one junction.

Various passivation region materials are contemplated for use, and anysuch material capable of providing the desired isolation properties isconsidered to be within the present scope. Non-limiting examples of suchmaterials include oxides, nitrides, oxynitrides, and the like, includingcombinations thereof. In one specific aspect the passivation regionincludes an oxide. Furthermore, various physical configurations for thepassivation region are also contemplated. In one aspect, for example,the passivation region is coupled directly to the at least one junction.In another aspect, the passivation region has a thickness of from about5 nm to about 100 nm. In yet another aspect, the passivation region hasa thickness of from about 20 nm to about 50 nm.

Additional regions and/or structures can be included in various devicesaccording to aspects present disclosure. In some aspects, for example,the device can include a reflecting region positioned to reflectelectromagnetic radiation passing through the textured region backthrough the textured region. Various reflective materials can beincluded in the reflecting region including, without limitation, a Braggreflector, a metal reflector, a metal reflector over a dielectricmaterial, and the like, including combinations thereof. In some aspects,a dielectric layer is positioned between the reflecting region and thetextured region. In another aspect, a lens can be optically coupled tothe semiconductor substrate and positioned to focus incidentelectromagnetic radiation into the semiconductor substrate.

Various materials can be utilized in the formation of the texturedregion, and any material capable of being associated with aphotosensitive imager and textured is considered to be within thepresent scope. One general non-limiting example includes a dielectricmaterial. Another example includes a polysilicon material.

In some cases the textured region can have a surface morphology operableto direct electromagnetic radiation into the semiconductor substrate.Non-limiting examples of textured region surface morphology includessloping, pyramidal, inverted pyramidal, spherical, square, rectangular,parabolic, asymmetric, symmetric, and combinations thereof.Additionally, various aspects of the textured region can vary dependingon the desired configuration of the device. In one aspect, for example,the textured region includes micron-sized and/or nano-sized surfacefeatures. Non-limiting examples of surface feature morphologies arecontemplated, nonlimiting examples of which include cones, pillars,pyramids, micolenses, quantum dots, inverted features, gratings, and thelike, including combinations thereof. Additionally, the textured regioncan be formed by a variety of processes, non-limiting examples of whichinclude plasma etching, reactive ion etching, porous silicon etching,lasing, chemical etching (e.g. anisotropic etching, isotropic etching),nanoimprinting, material deposition, selective epitaxial growth, and thelike, including combinations thereof.

In another aspect of the present disclosure, a backside-illuminatedphotosensitive imager array is provided. Such an array can include atleast two photosensitive imager devices as has been described. In oneaspect, at least one isolation feature is positioned between the atleast two photosensitive imager devices. In yet another aspect, the atleast one isolation feature is configured to optically or electricallyisolate the at least two photosensitive imager devices. In still anotherexample, the isolation feature can be a shallow or deep trench isolationfeature.

The present disclosure also provides methods of makingbackside-illuminated photosensitive imager devices. For example, in oneaspect such a method can include forming at least one junction at asurface of a semiconductor substrate, forming a passivation region overthe at least one junction, and forming a textured region over thepassivation region. The passivation region isolates the at least onejunction from the textured region, and the semiconductor substrate andthe textured region are positioned such that incoming electromagneticradiation passes through the semiconductor substrate before contactingthe textured region. The method additionally includes coupling anelectrical transfer element to the semiconductor substrate such that theelectrical transfer element is operable to transfer an electrical signalfrom the at least one junction. In another aspect, forming the texturedregion further includes depositing a semiconductor material on thepassivation region and texturing the semiconductor material to form thetextured region. In yet another aspect, forming the textured regionfurther includes depositing a dielectric material on the passivationregion and texturing the dielectric material to form the texturedregion.

The present disclosure additionally provides a backside-illuminatedphotosensitive imager device including a semiconductor substrate havingmultiple doped regions forming a least one junction, a textured regioncoupled to the semiconductor substrate and positioned to interact withelectromagnetic radiation, and a passivation region positioned betweenthe textured region and the at least one junction. The passivationregion is positioned to isolate the at least one junction from thetextured region, and the semiconductor substrate and the textured regionare positioned such that incoming electromagnetic radiation passesthrough the semiconductor substrate before contacting the texturedregion. The device further includes at least one transistor coupled tothe semiconductor substrate and with at least one of the transistorselectrically coupled to the at least one junction.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantage of the presentinvention, reference is being made to the following detailed descriptionof preferred embodiments and in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of a four transistor active pixel sensorof a CMOS imager in accordance with one aspect of the presentdisclosure;

FIG. 2 is a schematic view of a photosensitive device in accordance withanother aspect of the present disclosure;

FIG. 3 is a schematic view of a photosensitive device in accordance withyet another aspect of the present disclosure;

FIG. 4 is a schematic view of electromagnetic radiation reflectionpatterns in accordance with a further aspect of the present disclosure;

FIG. 5 is a graph showing calculated absorption of infrared radiation ina thin silicon photodetector with light trapping and different amountsof light reflected back from the illuminated surface;

FIG. 6 is a schematic view of a photosensitive device in accordance withanother aspect of the present disclosure;

FIG. 7 is a schematic view of a photosensitive device in accordance withanother aspect of the present disclosure;

FIG. 8 is a schematic view of a photosensitive device in accordance withyet another aspect of the present disclosure;

FIG. 9 is a schematic view of a photosensitive device in accordance witha further aspect of the present disclosure;

FIG. 10 is a schematic view of a photosensitive imager device inaccordance with yet another aspect of the present disclosure; and

FIG. 11 is a depiction of a method of making a photosensitive imagerdevice in accordance with yet another aspect of the present disclosure.

DETAILED DESCRIPTION

Before the present disclosure is described herein, it is to beunderstood that this disclosure is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting.

DEFINITIONS

The following terminology will be used in accordance with thedefinitions set forth below.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” and, “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a dopant” includes one or more of such dopants andreference to “the layer” includes reference to one or more of suchlayers.

As used herein, the terms “disordered surface” and “textured surface”can be used interchangeably, and refer to a surface having a topologywith nano- to micron-sized surface variations formed by the irradiationof laser pulses or other texturing methods such as chemical etching asdescribed herein. While the characteristics of such a surface can bevariable depending on the materials and techniques employed, in oneaspect such a surface can be several hundred nanometers thick and madeup of nanocrystallites (e.g. from about 10 to about 50 nanometers) andnanopores. In another aspect, such a surface can include micron-sizedstructures (e.g. about 2 μm to about 60 μm). In yet another aspect, thesurface can include nano-sized and/or micron-sized structures from about5 nm and about 500 μm.

As used herein, the term “fluence” refers to the amount of energy from asingle pulse of laser radiation that passes through a unit area. Inother words, “fluence” can be described as the energy density of onelaser pulse.

As used herein, the terms “surface modifying” and “surface modification”refer to the altering of a surface of a semiconductor material using avariety of surface modification techniques. Non-limiting examples ofsuch techniques include plasma etching, reactive ion etching, poroussilicon etching, lasing, chemical etching (e.g. anisotropic etching,isotropic etching), nanoimprinting, material deposition, selectiveepitaxial growth, and the like, including combinations thereof. In onespecific aspect, surface modification can include processes usingprimarily laser radiation or laser radiation in combination with adopant, whereby the laser radiation facilitates the incorporation of thedopant into a surface of the semiconductor material. Accordingly, in oneaspect surface modification includes doping of a substrate such as asemiconductor material.

As used herein, the term “target region” refers to an area of asubstrate that is intended to be doped or surface modified. The targetregion of the substrate can vary as the surface modifying processprogresses. For example, after a first target region is doped or surfacemodified, a second target region may be selected on the same substrate.

As used herein, the term “detection” refers to the sensing, absorption,and/or collection of electromagnetic radiation.

As used herein, the term “backside illumination” refers to a devicearchitecture design whereby electromagnetic radiation is incident on asurface of a semiconductor material that is opposite a surfacecontaining the device circuitry. In other words, electromagneticradiation is incident upon and passes through a semiconductor materialprior to contacting the device circuitry.

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. For example, an object that is“substantially” enclosed would mean that the object is either completelyenclosed or nearly completely enclosed. The exact allowable degree ofdeviation from absolute completeness may in some cases depend on thespecific context. However, generally speaking the nearness of completionwill be so as to have the same overall result as if absolute and totalcompletion were obtained. The use of “substantially” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result. For example, a composition that is“substantially free of” particles would either completely lackparticles, or so nearly completely lack particles that the effect wouldbe the same as if it completely lacked particles. In other words, acomposition that is “substantially free of” an ingredient or element maystill actually contain such item as long as there is no measurableeffect thereof.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 to about 5” should beinterpreted to include not only the explicitly recited values of about 1to about 5, but also include individual values and sub-ranges within theindicated range. Thus, included in this numerical range are individualvalues such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4,and from 3-5, etc., as well as 1, 2, 3, 4, and 5, individually.

This same principle applies to ranges reciting only one numerical valueas a minimum or a maximum. Furthermore, such an interpretation shouldapply regardless of the breadth of the range or the characteristicsbeing described.

The Disclosure

Electromagnetic radiation can be present across a broad wavelengthrange, including visible range wavelengths (approximately 350 nm to 800nm) and non-visible wavelengths (longer than about 800 nm or shorterthan 350 nm). The infrared spectrum is often described as including anear infrared portion of the spectrum including wavelengths ofapproximately 800 to 1300 nm, a short wave infrared portion of thespectrum including wavelengths of approximately 1300 nm to 3micrometers, and a mid to long wave infrared (or thermal infrared)portion of the spectrum including wavelengths greater than about 3micrometers up to about 30 micrometers. These are generally andcollectively referred to herein as “infrared” portions of theelectromagnetic spectrum unless otherwise noted.

Traditional silicon photodetecting imagers have limited lightabsorption/detection properties. For example, such silicon baseddetectors are mostly transparent to infrared light. While other mostlyopaque materials (e.g. InGaAs) can be used to detect infraredelectromagnetic radiation having wavelengths greater than about 1000 nm,silicon is still commonly used because it is relatively cheap tomanufacture and can be used to detect wavelengths in the visiblespectrum (i.e. visible light, 350 nm-800 nm). Traditional siliconmaterials require substantial path lengths and absorption depths todetect photons having wavelengths longer than approximately 700 nm.While visible light can be absorbed at relatively shallow depths insilicon, absorption of longer wavelengths (e.g. 900 nm) in silicon of astandard wafer depth (e.g. approximately 750 μm) is poor if at all.

The devices of the present disclosure increase the absorption ofsemiconductor materials by increasing the absorption path length forlonger wavelengths as compared to traditional materials. The absorptiondepth in conventional silicon detectors is the depth into silicon atwhich the radiation intensity is reduced to about 36% of the value atthe surface of the semiconductor. The increased absorption path lengthresults in an apparent reduction in the absorption depth, or a reducedapparent or effective absorption depth. For example, the effectiveabsorption depth of silicon can be reduced such that these longerwavelengths can be absorbed at depths of less than or equal to about 850μm. In other words, by increasing the absorption path length, thesedevices are able to absorb longer wavelengths (e.g. >1000 nm forsilicon) within a thin semiconductor material. In addition to decreasingthe effective absorption depth, the response rate or response speed canalso be increased using thinner semiconductor materials.

Accordingly, backside-illuminated (BSI) photosensitive imager devicesand associated methods are provided. Such devices provide, among otherthings, enhanced response in the near infrared light portion of theoptical spectrum and improved response and quantum efficiency inconverting electromagnetic radiation to electrical signals. As such,quantum efficiency (QE) of over 60% can be obtained in the visibleregion. Quantum efficiency can be defined as the percentage of photonsthat are converted into electrons. There are two types of QE, internaland external. Internal QE (IQE) describes the percentage of absorbedphotons that are converted into electrons within the device. External QE(EQE) is the measurement of this conversion and the electrons that arecollected outside of the device. The EQE is always lower than the IQEsince there will inevitably be recombination effects and optical losses(e.g. transmission and reflection losses). One reason for improvedperformance with BSI is a higher fill factor or, in other words, theamount of light that can be collected in a single pixel. The variousmetal layers on top of a front side-illuminated sensor (FSI) limit theamount of light that can be collected in a pixel. As pixel sizes getsmaller, the fill factor gets worse. BSI provides a more direct path forlight to travel into the pixel, thus avoiding light blockage by themetal interconnect and dielectric layers on the top-side of thesemiconductor substrate.

The present disclosure additionally provides BSI broadbandphotosensitive diodes, pixels, and imagers capable of detecting visibleas well as infrared electromagnetic radiation, including associatedmethods of making such devices. A photosensitive diode can include asemiconductor substrate having multiple doped regions forming at leastone junction, a textured region coupled to the semiconductor substrateand positioned to interact with electromagnetic radiation, and apassivation region positioned between the textured region and the atleast one junction. The passivation region is positioned to isolate theat least one junction from the textured region, and the semiconductorsubstrate and the textured region are positioned such that incomingelectromagnetic radiation passes through the semiconductor substratebefore contacting the textured region.

In one aspect the multiple doped regions can include at least onecathode region and at least one anode region. In some aspects, dopedregions can include an n-type dopant and/or a p-type dopant as isdiscussed below, thereby creating a p-n junction. In other aspects, aphotosensitive device can include an i-type region to form a p-i-njunction.

A photosensitive pixel can include a semiconductor substrate havingmultiple doped regions forming at least one junction, a textured regioncoupled to the semiconductor substrate and positioned to interact withelectromagnetic radiation, and a passivation region positioned betweenthe textured region and the at least one junction. The passivationregion is positioned to isolate the at least one junction from thetextured region, and the semiconductor substrate and the textured regionare positioned such that incoming electromagnetic radiation passesthrough the semiconductor substrate before contacting the texturedregion. Additionally, the photosensitive pixel also includes anelectrical transfer element coupled to the semiconductor substrate andoperable to transfer an electrical signal from the at least onejunction. A photosensitive imager can include multiple photosensitivepixels. Additionally, an electrical transfer element can include avariety of devices, including without limitation, transistors, sensingnodes, transfer gates, transfer electrodes, and the like.

Photosensitive or photo detecting imagers include photodiodes or pixelsthat are capable of absorbing electromagnetic radiation within a givenwavelength range. Such imagers can be passive pixel sensors (PPS),active pixel sensors (APS), digital pixel sensor imagers (DPS), or thelike, with one difference being the image sensor read out architecture.For example, a semiconducting photosensitive imager can be a three orfour transistor active pixel sensor (3T APS or 4T APS). Variousadditional components are also contemplated, and would necessarily varydepending on the particular configuration and intended results. As anexample, a 4T configuration as is shown in FIG. 1 can additionallyinclude, among other things, a transfer gate 2, a reset transistor 1, asource follower 3, a row select transistor 4, and a photodiode sensor 5.Additionally, devices having greater than 4 transistors are also withinthe present scope. Photosensor diode 5 can be a conventional pinnedphotodiode as used in current state of the art CMOS imagers.

As has been described, photosensitive imagers can be front sideillumination (FSI) or back side illumination (BSI) devices. In a typicalFSI imager, incident light enters the semiconductor device by firstpassing by transistors and metal circuitry. The light, however, canscatter off of the transistors and circuitry prior to entering the lightsensing portion of the imager, thus causing optical loss and noise. Alens can be disposed on the topside of a FSI pixel to direct and focusthe incident light to the light sensing active region of the device,thus partially avoiding the circuitry. In one aspect the lens can be amicro-lens. BSI imagers, one the other hand, are configured to have thedepletion region of the junction extending to the opposite side of thedevice. In one aspect, for example, incident light enters the device viathe light sensing portion and is mostly absorbed prior to reaching thecircuitry. BSI designs allow for smaller pixel architecture and a highfill factor for the imager. It should also be understood that devicesaccording to aspects of the present disclosure can be incorporated intocomplimentary metal-oxide-semiconductor (CMOS) imager architectures orcharge-coupled device (CCD) imager architectures.

In one aspect, as is shown in FIG. 2, a BSI photosensitive diode 20 caninclude a semiconductor substrate 22 having multiple doped regions 23,24 forming at least one junction, and a textured region 28 coupled tothe semiconductor substrate and positioned to interact withelectromagnetic radiation. The multiple doped regions can have the samedoping profile or different doping profiles, depending on the device.While the device shown in FIG. 2 contains three doped regions, it shouldbe noted that other aspects containing one or more doped regions areconsidered to be within the present scope. Additionally, thesemiconductor substrate can be doped, and thus can be considered to be adoped region in some aspects. A passivation region 26 is positionedbetween the textured region and the at least one junction. In oneembodiment the passivation region can have a thickness in the range ofabout 10 nm to about 2 μm. In another embodiment the passivation regioncan have a thickness in the range of about 10 nm to about 100 nm. In yetanother embodiment the passivation region can have a thickness of lessthan 50 nm. The passivation region is positioned to isolate the at leastone junction from the textured region, and the semiconductor substrateand the textured region are positioned such that incomingelectromagnetic radiation passes through the semiconductor substratebefore contacting the textured region. The photosensitive diode isbackside illuminated by electromagnetic radiation 29 that is incident onthe side of the semiconductor substrate opposite the multiple dopedregions.

In another aspect, as is shown in FIG. 3, a BSI photosensitive imagerdevice 30 is provided. The BSI photosensitive imager device includes asemiconductor substrate 32 having multiple doped regions 33, 34 forminga least one junction, and a textured region 38 coupled to thesemiconductor substrate and positioned to interact with electromagneticradiation. A passivation region 36 is positioned between the texturedregion and the at least one junction to isolate the at least onejunction from the textured region. The semiconductor substrate and thetextured region are positioned such that incoming electromagneticradiation 39 passes through the semiconductor substrate beforecontacting the textured region. An electrical transfer element 37 iscoupled to the semiconductor substrate to transfer an electrical signalfrom the at least one junction. Side wall insulators 51 and 52 can alsobe formed about the transfer element 37 and passivation/texturedregions, respectively, to insure proper spacing away from the transferelement. Additionally, a drain junction region 53 is electrically iselectrically coupled to the transfer element to receive chargetransferred thereto by the transfer element.

The various devices according to aspects of the present disclosure canexhibit increased quantum efficiency over traditional photosensitivedevices. Any increase in the quantum efficiency makes a large differencein the signal to noise ratio. More complex structures can provide notonly increased quantum efficiency but also good uniformity from pixel topixel. In addition, devices of the present disclosure exhibit increasedresponsivity as compared to traditional photosensitive devices. Forexample, in one aspect the responsivity can be greater than or equal to0.8 A/W for wavelengths greater than 1000 nm for semiconductor substratethat is less than 100 μm thick. In other embodiment the responsivity canbe greater than 0.5 A/W for wavelengths greater than 1100 nm forsemiconductor substrate that is less than 50 μm thick.

A variety of semiconductor materials are contemplated for use with thedevices and methods according to aspects of the present disclosure.Non-limiting examples of such semiconductor materials can include groupIV materials, compounds and alloys comprised of materials from groups IIand VI, compounds and alloys comprised of materials from groups III andV, and combinations thereof. More specifically, exemplary group IVmaterials can include silicon, carbon (e.g. diamond), germanium, andcombinations thereof. Various exemplary combinations of group IVmaterials can include silicon carbide (SiC) and silicon germanium(SiGe). In one specific aspect, the semiconductor material can be orinclude silicon. Exemplary silicon materials can include amorphoussilicon (a-Si), microcrystalline silicon, multicrystalline silicon, andmonocrystalline silicon, as well as other crystal types. In anotheraspect, the semiconductor material can include at least one of silicon,carbon, germanium, aluminum nitride, gallium nitride, indium galliumarsenide, aluminum gallium arsenide, and combinations thereof.

Exemplary combinations of group II-VI materials can include cadmiumselenide (CdSe), cadmium sulfide (CdS), cadmium telluride (CdTe), zincoxide (ZnO), zinc selenide (ZnSe), zinc sulfide (ZnS), zinc telluride(ZnTe), cadmium zinc telluride (CdZnTe, CZT), mercury cadmium telluride(HgCdTe), mercury zinc telluride (HgZnTe), mercury zinc selenide(HgZnSe), and combinations thereof.

Exemplary combinations of group III-V materials can include aluminumantimonide (AlSb), aluminum arsenide (AlAs), aluminum nitride (AlN),aluminum phosphide (AlP), boron nitride (BN), boron phosphide (BP),boron arsenide (BAs), gallium antimonide (GaSb), gallium arsenide(GaAs), gallium nitride (GaN), gallium phosphide (GaP), indiumantimonide (InSb), indium arsenide (InAs), indium nitride (InN), indiumphosphide (InP), aluminum gallium arsenide (AlGaAs, Al_(x)Ga_(1-x)As),indium gallium arsenide (InGaAs, In_(x)Ga_(1-x)As), indium galliumphosphide (InGaP), aluminum indium arsenide (AlInAs), aluminum indiumantimonide (AlInSb), gallium arsenide nitride (GaAsN), gallium arsenidephosphide (GaAsP), aluminum gallium nitride (AlGaN), aluminum galliumphosphide (AlGaP), indium gallium nitride (InGaN), indium arsenideantimonide (InAsSb), indium gallium antimonide (InGaSb), aluminumgallium indium phosphide (AlGaInP), aluminum gallium arsenide phosphide(AlGaAsP), indium gallium arsenide phosphide (InGaAsP), aluminum indiumarsenide phosphide (AlInAsP), aluminum gallium arsenide nitride(AlGaAsN), indium gallium arsenide nitride (InGaAsN), indium aluminumarsenide nitride (InAlAsN), gallium arsenide antimonide nitride(GaAsSbN), gallium indium nitride arsenide antimonide (GaINAsSb),gallium indium arsenide antimonide phosphide (GaInAsSbP), andcombinations thereof.

The semiconductor substrate can be of any thickness that allowselectromagnetic radiation detection and conversion functionality, andthus any such thickness of semiconductor material is considered to bewithin the present scope. In some aspects the textured region increasesthe efficiency of the device such that the semiconductor substrate canbe thinner than has previously been possible. Decreasing the thicknessof the semiconductor substrate reduces the amount of semiconductormaterial required to make such a device. In one aspect, for example, thesemiconductor substrate has a thickness of from about 500 nm to about 50μm. In another aspect, the semiconductor substrate has a thickness ofless than or equal to about 100 μm. In yet another aspect, thesemiconductor substrate has a thickness of from about 1 μm to about 10μm. In a further aspect, the semiconductor substrate can have athickness of from about 5 μm to about 50 μm. In yet a further aspect,the semiconductor substrate can have a thickness of from about 5 μm toabout 10 μm.

Additionally, various types of semiconductor materials are contemplated,and any such material that can be incorporated into an electromagneticradiation detection device is considered to be within the present scope.In one aspect, for example, the semiconductor material ismonocrystalline. In another aspect, the semiconductor material ismulticrystalline. In yet another aspect, the semiconductor material ismicrocrystalline. It is also contemplated that the semiconductormaterial can be amorphous. Specific nonlimiting examples includeamorphous silicon or amorphous selenium.

The semiconductor materials of the present disclosure can also be madeusing a variety of manufacturing processes. In some cases themanufacturing procedures can affect the efficiency of the device, andmay be taken into account in achieving a desired result. Exemplarymanufacturing processes can include Czochralski (Cz) processes, magneticCzochralski (mCz) processes, Float Zone (FZ) processes, epitaxial growthor deposition processes, and the like. It is contemplated that thesemiconductor materials used in the present invention can be acombination of monocrystalline material with epitaxially grown layersformed thereon.

The textured region can function to diffuse electromagnetic radiation,to redirect electromagnetic radiation, and to absorb electromagneticradiation, thus increasing the quantum efficiency of the device. In thepresent BSI devices, electromagnetic radiation passing through thesemiconductor substrate can contact the textured region. The texturedregion can include surface features to thus increase the effectiveabsorption length of the photosensitive pixel. Such surface features canbe micron-sized and/or nano-sized, and can be any shape orconfigurations. Non-limiting examples of such shapes and configurationsinclude cones, pillars, pyramids, micolenses, quantum dots, invertedfeatures, gratings, protrusions, and the like, including combinationsthereof. Additionally, factors such as manipulating the feature sizes,dimensions, material type, dopant profiles, texture location, etc. canallow the diffusing region to be tunable for a specific wavelength. Inone aspect, tuning the device can allow specific wavelengths or rangesof wavelengths to be absorbed. In another aspect, tuning the device canallow specific wavelengths or ranges of wavelengths to be reduced oreliminated via filtering.

Tuning can also be accomplished through the relative location of thetexture region within the device, modifying the dopant profile(s) ofregions within the device, dopant selection, and the like. Additionally,material composition near the textured region can create a wavelengthspecific photosensing pixel device. It should be noted that a wavelengthspecific photosensing pixel can differ from one pixel to the next, andcan be incorporated into an imaging array. For example a 4×4 array caninclude a blue pixel, a green pixel, a red pixel, and infrared lightabsorbing pixel, or a blue pixel, two green pixels, and a red pixel.

Textured regions according to aspects of the present disclosure canallow a photosensitive device to experience multiple passes of incidentelectromagnetic radiation within the device, particularly at longerwavelengths (i.e. infrared). Such internal reflection increases theeffective absorption length to be greater than the thickness of thesemiconductor substrate. This increase in absorption length increasesthe quantum efficiency of the device, leading to an improved signal tonoise ratio.

The materials used for making the textured region can vary depending onthe design and the desired characteristics of the device. As such, anymaterial that can be utilized in the construction of a textured regionis considered to be within the present scope. Non-limiting examples ofsuch materials include semiconductor materials, dielectric materials,silicon, polysilicon, amorphous silicon, transparent conductive oxides,and the like, including composites and combinations thereof. In onespecific aspect, the textured layer is a textured polysilicon layer.Thus a polysilicon layer can be deposited onto the passivation region,and then textured to form the textured region. In another aspect, thetextured layer is a textured dielectric layer. In this case the texturedregion is a portion of the dielectric layer making up the passivationregion. In yet another aspect the textured layer is a transparentconductive oxide or another semiconductor material. In the case ofdielectric layers, the textured region can be a textured portion of thepassivation region or the textured region can be formed from otherdielectric material deposited over the passivation region. In the caseof semiconductor materials, forming the textured region can includedepositing a semiconductor material on the passivation region andtexturing the semiconductor material to form the textured region. Thetexturing process can texture the entire semiconductor material or onlya portion of the semiconductor material. In one specific aspect, apolysilicon layer can be deposited over the passivation layer andtextured and patterned by an appropriate technique (e.g. a poroussilicon etch) to form the texture region. In yet another aspect, apolysilicon layer can be deposited over the passivation layer andtextured and patterned by using a mask and photolithography and an etchto define a specific structure or pattern.

In addition to surface features, the textured region can have a surfacemorphology that is designed to focus or otherwise direct electromagneticradiation. For example, in one aspect the textured region has a surfacemorphology operable to direct electromagnetic radiation into thesemiconductor substrate. Non-limiting examples of various surfacemorphologies include sloping, pyramidal, inverted pyramidal, spherical,square, rectangular, parabolic, asymmetric, symmetric, and the like,including combinations thereof.

One example of such a surface morphology is shown in FIG. 4. Withoutintending to be limited to any operational theory, the followingdescription provides one possible explanation for the effects of surfacemorphology on the direction of electromagnetic radiation. FIG. 4 shows atextured device having a surface morphology that affects the nearinfrared wavelength response. A semiconductor substrate 40 is shownhaving an illuminated surface 42 to receive incident electromagneticradiation. The semiconductor substrate further has a textured region 44(e.g. dielectric) coupled thereto at a surface that is opposite to theilluminated surface. The textured region has a surface morphologyconfigured in an undulating pattern 46 with grooves, ridges, or similarpatterns to produce an internal reflection that is not specular. In thenear infrared the index of refraction of silicon is about η=3.42 and thereflectance is about R=30% from a single surface, and transmittancethrough a single surface is T=70% for normal incident waves. Theabsorption coefficient of silicon is very low in the near infrared.Electromagnetic radiation under normal incidence, represented by arrow48, is reflected from the illuminated surface 42, and this is shown asarrow 41. There are successive reflections from both the illuminatedsurface and the opposing side, represented by arrows 43 and 45, andinternal reflections from the illuminated surface, represented by arrow47, resulting in a total internal reflection, if there is neither areflective metal layer 49 nor textured region, the total transmittance,T_(tot), is as shown in Equation (I) as:

T _(tot)=(TT)(1+R ² +R ⁴+ . . . )=(TT)/(1−R ²)  (I)

This result has been obtained using the sum of a geometric series. Ifboth surfaces are just polished silicon-air then this results in a totaltransmittance of 54% and a reflectance of 46%.

If the increase in the individual path lengths caused by the diffusescattering is neglected and if the absorption coefficient is very lowthen the total effective path length is determined by just the number ofreflections, and the total absorption can be as shown in Equation (II):

A=αd(1+R ₂)(1+R ₁ R ₂ +R ₁ ² R ₂ ²+ . . . )=αd(1+R ₂)/(1−R ₁ R ₂)  (II)

Here, α, is the absorption coefficient in reciprocal cm and, d, is thethickness of the sample in cm, and the effective increase in path lengthis Enh=(1+R₂)/(1−R₁R₂). The internal quantum efficiency, IQE, in theinfrared where the absorption in silicon is low is then, IQE=αd(Enh).The external quantum efficiency, EQE, is EQE=T₁IQE and EQE=T₁αd(Enh).

If both sides of an infrared photo detector are polished then T₁=T₂=0.70and R₁=R₂=0.3, which gives Enh=1.4, IQE=1.4 αd and EQE=αd. If one sideis polished and the other side has an oxide and then a metal reflectorthen R1=0.3 and R2=1.0, this yields an enhancement in infraredabsorption or Enh=3. T₁, is the transmittance of radiation incident onthe first surface. T₂, is the transmittance of radiation striking thesecond surface from the semiconductor side. R₁ is the amount ofradiation reflected back into the semiconductor for radiation strikingthe first surface from the semiconductor side. R₂ is the amount ofradiation reflected back into the semiconductor for radiation strikingthe second surface from the semiconductor side.

In one aspect that can improve the infrared response, the illuminatedside 42 is polished but the opposing side 46 is a textured dielectricmaterial 44, with a reflecting region 49. The texturing can be realizedin a fashion to produce a true diffuse scattering (i.e. a Lambertianscattering), at the infrared wavelengths. This diffuse scatteringlayer/reflecting layer combination, in essence, yields an R₂=100%, adiffuse reflector. The reflectance of the polished front side to thescattered light radiation is determined by solid angle considerations.Any incident light with an angle of incidence greater than the criticalangle, θ 50, will be totally internal reflected, 47. If the backsidescattering is totally diffuse or Lambertian, the transmittance is thendetermined by the area of the surface, πr², within the critical angle θ(labeled 50), in this case 17° for silicon and air. The radius of thecircle is r=d sin(17), where, d, is the thickness of the sample. Thisarea is divided by the area of the half sphere, 2πd². If the backsidescattering is totally diffuse the transmittance of the front planarsurface is then roughly T₁=3% and the reflectance R₁=97%. The pathlength enhancement factor can be very large, as is shown in Equation(III):

Enh=(1+R ₂)/(1−R ₁ R ₂)=66  (III)

This would result in an IQE=66αd and an EQE=46. If the backside includesa textured region and a truly diffusive scattering surface and amirror-like surface is used behind the back side, a very largeenhancement of absorption in the near infrared can be achieved. If theabsorption in the semiconductor substrate is not assumed to be small butrather is taken into account it can be shown that the enhancement factorfor the IQE due to multiple reflections is modified from Equation (I)and as is shown in Equation (IV):

Enh=(1−exp(−αd))(1+R ₂exp(−αd))/(1−R ₁ R ₂exp(−2αd))  (IV)

This allows a calculation of the responsivity, in terms of theelectrical current in Amperes per incident light power in Watts, ofphoto detectors of different thickness, d, for different wavelengths, λ,since the absorption coefficient, α(λ), is a function of wavelength, asis shown in FIG. 5. If it is assumed that the textured side is an idealreflector, R₂=1.0, and the amount of diffusive scattering of thetextured surface varies from that of a planar surface, then the fractionof light reflected back from the opposing illuminated surface will vary.If the textured surface is planar, then there is only specularreflection, and R₁=0.3; if the textured surface is an ideal Lambertiandiffusive surface then the fraction of light reflected back from thefront surface will be very large, R₁=0.97. Several values of R₁ asillustrated by curves, 601, 602, and 603 are discussed herein, andillustrated in FIG. 5, for a diffuse reflector, and these represent thefraction of light internally reflected back at the front surface. Forpurposes of the present disclosure, values of R₁≧0.9, curve 601, aredeemed useful. The enhancement in absorption described by Equation (IV)then varies with the fraction of light radiation reflected back from theilluminated surface and thickness of the sample, as is illustrated inFIG. 5. It should be noted that, while the techniques described hereinhave been used to enhance the absorption of infrared and red lightradiation, they are also applicable to visible light as the thickness ofthe silicon layer becomes thinner Scattering and multiple internalreflections can also be used to increase the absorption of yellow, greenand even blue light that will not be totally absorbed in single passeswithin thin silicon layers. These techniques can be applied then tovisible imagers with thin silicon absorption layers.

The textured region, including surface features as well as surfacemorphologies, can be formed by various techniques, including plasmaetching, reactive ion etching, porous silicon etching, lasing, chemicaletching (e.g. anisotropic etching, isotropic etching), nanoimprinting,material deposition, selective epitaxial growth, and the like. In oneaspect, the texturing process can be performed during the manufacture ofthe photosensitive device. In another aspect, the texturing process canbe performed on a photosensitive device that has previously been made.For example, a CMOS, CCD, or other photosensitive element can betextured following manufacture. In this case, material layers may beremoved from the photosensitive element to expose the semiconductorsubstrate or the passivation region upon which a textured region can beformed.

One effective method of producing a textured region is through laserprocessing. Such laser processing allows discrete locations of thepassivation region or other substrate to be textured. A variety oftechniques of laser processing to form a textured region arecontemplated, and any technique capable of forming such a region shouldbe considered to be within the present scope. Laser treatment orprocessing can allow, among other things, enhanced absorption propertiesand thus increased electromagnetic radiation focusing and detection. Thelaser treated region can be associated with the surface nearest theimpinging electromagnetic radiation or, in the case of BSI devices, thelaser treated surface can be associated with a surface opposite inrelation to impinging electromagnetic radiation, thereby allowing theradiation to pass through the semiconductor substrate before it hits thelaser treated region.

In one aspect, for example, a target region of the semiconductormaterial can be irradiated with laser radiation to form a texturedregion. Examples of such processing have been described in furtherdetail in U.S. Pat. Nos. 7,057,256, 7,354,792 and 7,442,629, which areincorporated herein by reference in their entireties. Briefly, a surfaceof a substrate material is irradiated with laser radiation to form atextured or surface modified region. Such laser processing can occurwith or without a dopant material. In those aspects whereby a dopant isused, the laser can be directed through a dopant carrier and onto thesubstrate surface. In this way, dopant from the dopant carrier isintroduced into the target region of the substrate material. Such aregion incorporated into a substrate material can have various benefitsin accordance with aspects of the present disclosure. For example, thetarget region typically has a textured surface that increases thesurface area of the laser treated region and increases the probabilityof radiation absorption via the mechanisms described herein. In oneaspect, such a target region is a substantially textured surfaceincluding micron-sized and/or nano-sized surface features that have beengenerated by the laser texturing. In another aspect, irradiating thesurface of the substrate material includes exposing the laser radiationto a dopant such that irradiation incorporates the dopant into thesubstrate. Various dopant materials are known in the art, and arediscussed in more detail herein.

Thus the surface of the substrate or passivation region is chemicallyand/or structurally altered by the laser treatment, which may, in someaspects, result in the formation of surface features appearing asmicrostructures or patterned areas on the surface and, if a dopant isused, the incorporation of such dopants into the substrate material. Insome aspects, the features or microstructures can be on the order of 50nm to 20 μm in size and can assist in the absorption of electromagneticradiation. In other words, the textured surface can increase theprobability of incident radiation being absorbed.

The type of laser radiation used to surface modify a material can varydepending on the material and the intended modification. Any laserradiation known in the art can be used with the devices and methods ofthe present disclosure. There are a number of laser characteristics,however, that can affect the surface modification process and/or theresulting product including, but not limited to the wavelength of thelaser radiation, pulse width, pulse fluence, pulse frequency,polarization, laser propagation direction relative to the semiconductormaterial, etc. In one aspect, a laser can be configured to providepulsatile lasing of a material. A short-pulsed laser is one capable ofproducing femtosecond, picosecond and/or nanosecond pulse durations.Laser pulses can have a central wavelength in a range of about fromabout 10 nm to about 8 μm, and more specifically from about 200 nm toabout 1200 nm. The pulse width of the laser radiation can be in a rangeof from about tens of femtoseconds to about hundreds of nanoseconds. Inone aspect, laser pulse widths can be in the range of from about 50femtoseconds to about 50 picoseconds. In another aspect, laser pulsewidths can be in the range of from about 50 picoseconds to 100nanoseconds. In another aspect, laser pulse widths are in the range offrom about 50 to 500 femtoseconds.

The number of laser pulses irradiating a target region can be in a rangeof from about 1 to about 2000. In one aspect, the number of laser pulsesirradiating a target region can be from about 2 to about 1000. Further,the repetition rate or frequency of the pulses can be selected to be ina range of from about 10 Hz to about 10 μHz, or in a range of from about1 kHz to about 1 MHz, or in a range from about 10 Hz to about 1 kHz.Moreover, the fluence of each laser pulse can be in a range of fromabout 1 kJ/m² to about 20 kJ/m², or in a range of from about 3 kJ/m² toabout 8 kJ/m².

A variety of dopant materials are contemplated for both the formation ofthe multiple doped regions and incorporation by a texturing technique,and any such dopant that can be used in such processes to surface modifya material is considered to be within the present scope. It should benoted that the particular dopant utilized can vary depending on thematerial being doped, as well as the intended use of the resultingmaterial. For example, the selection of potential dopants may differdepending on whether or not tuning of the photosensitive device isdesired.

A dopant can be either charge donating or accepting dopant species. Morespecifically, an electron donating or a hole donating species can causea region to become more positive or negative in polarity as compared tothe semiconductor substrate. In one aspect, for example, the dopedregion can be p-doped. In another aspect the doped region can ben-doped. A highly doped region can also be formed on or near the dopedregion to create a pinned diode. In one non-limiting example, thesemiconductor substrate can be negative in polarity, and a doped regionand a highly doped region can be doped with p+ and n dopantsrespectively. In some aspects, variations of n(−−), n(−), n(+), n(++),p(−−), p(−), p(+), or p(++) type doping of the regions can be used. Itshould be noted that in one aspect the highly doped region can be atextured region. In other words, textured surface features can be formedon or in a highly doped region. In another aspect, at least a portion ofthe textured region, or the material from which the textured region isgenerated, can be doped with a dopant to generate a back surface field.A back surface field can function to impede the movement ofphoto-generated carriers from the junction toward the textured region.

In one aspect, non-limiting examples of dopant materials can include S,F, B, P, N, As, Se, Te, Ge, Ar, Ga, In, Sb, and combinations thereof. Itshould be noted that the scope of dopant materials should include, notonly the dopant materials themselves, but also materials in forms thatdeliver such dopants (i.e. dopant carriers). For example, S dopantmaterials includes not only S, but also any material capable being usedto dope S into the target region, such as, for example, H₂S, SF₆, SO₂,and the like, including combinations thereof. In one specific aspect,the dopant can be S. Sulfur can be present at an ion dosage level ofbetween about 5×10¹⁴ and about 1×10¹⁶ ions/cm². Non-limiting examples offluorine-containing compounds can include ClF₃, PF₅, F₂SF₆, BF₃, GeF₄,WF₆, SiF₄, HF, CF₄, CHF₃, CH₂F₂, CH₃F, C₂F₆, C₂HF₅, C₃F₈, C₄F₈, NF₃, andthe like, including combinations thereof. Non-limiting examples ofboron-containing compounds can include B(CH₃)₃, BF₃, BCl₃, BN, C₂B₁₀H₁₂,borosilica, B₂H₆, and the like, including combinations thereof.Non-limiting examples of phosphorous-containing compounds can includePF₅, PH₃, and the like, including combinations thereof. Non-limitingexamples of chlorine-containing compounds can include Cl₂, SiH₂Cl₂, HCl,SiCl₄, and the like, including combinations thereof. Dopants can alsoinclude arsenic-containing compounds such as AsH₃ and the like, as wellas antimony-containing compounds. Additionally, dopant materials caninclude mixtures or combinations across dopant groups, i.e. asulfur-containing compound mixed with a chlorine-containing compound. Inone aspect, the dopant material can have a density that is greater thanair. In one specific aspect, the dopant material can include Se, H₂S,SF₆, or mixtures thereof. In yet another specific aspect, the dopant canbe SF₆ and can have a predetermined concentration range of about5.0×10⁻⁸ mol/cm³ to about 5.0×10⁻⁴ mol/cm³. As one non-limiting example,SF₆ gas is a good carrier for the incorporation of sulfur into thesemiconductor material via a laser process without significant adverseeffects on the material. Additionally, it is noted that dopants can alsobe liquid solutions of n-type or p-type dopant materials dissolved in asolution such as water, alcohol, or an acid or basic solution. Dopantscan also be solid materials applied as a powder or as a suspension driedonto the wafer.

As a further processing note, the semiconductor substrate can beannealed for a variety of reasons, including dopant activation,semiconductor damage repair, and the like. The semiconductor substratecan be annealed prior to texturing, following texturing, duringtexturing, or any combination thereof. Annealing can enhance thesemiconductive properties of the device, including increasing thephotoresponse properties of the semiconductor materials by reducing anyimperfections in the material. Additionally, annealing can reduce damagethat may occur during the texturing process. Although any known annealcan be beneficial and would be considered to be within the presentscope, annealing at lower temperatures can be particularly useful. Sucha “low temperature” anneal can greatly enhance the external quantumefficiency of devices utilizing such materials. In one aspect, forexample, the semiconductor substrate can be annealed to a temperature offrom about 300° C. to about 1100 C.°. In another aspect, thesemiconductor substrate can be annealed to a temperature of from about500° C. to about 900° C. In yet another aspect, the semiconductorsubstrate can be annealed to a temperature of from about 700° C. toabout 800° C. In a further aspect, the semiconductor substrate can beannealed to a temperature that is less than or equal to about 850° C.

The duration of the annealing procedure can vary according to thespecific type of anneal being performed, as well as according to thematerials being used. For example, rapid annealing processes can beused, and as such, the duration of the anneal may be shorter as comparedto other techniques. Various rapid thermal anneal techniques are known,all of which should be considered to be within the present scope. In oneaspect, the semiconductor substrate can be annealed by a rapid annealingprocess for a duration of greater than or equal to about 1 μs. Inanother aspect, the duration of the rapid annealing process can be fromabout 1 μs to about 1 ms. As another example, a baking or furnace annealprocess can be used having durations that may be longer compared to arapid anneal. In one aspect, for example, the semiconductor substratecan be annealed by a baking anneal process for a duration of greaterthan or equal to about 1 ms to several hours.

Various types of passivation region configurations are contemplated, andany configuration that can be incorporated into a photosensitive deviceis considered to be within the present scope. One benefit to such apassivation region pertains to the isolation provided between thetextured region and the doped regions that form the junction. In oneaspect, for example, the passivation region can be positioned tophysically isolate the textured region from the junction. In this way,the creation of the textured region can be isolated from the dopedregions, thus precluding undesirable effects of the texturing processfrom affecting the junction. In another aspect, the passivation regioncan be a dielectric material, and thus the passivation region could beused to electrically isolate the textured region from the junction. Insome cases, the passivation region is coupled directly to at least oneof the doped regions forming the junction.

The passivation region can be made from a variety of materials, and suchmaterials can vary depending on the device design and desiredcharacteristics. Non-limiting examples of such materials can includeoxides, nitrides, oxynitrides, and the like, including combinationsthereof. In one specific aspect, the passivation region includes anoxide. Additionally, the passivation region can be of variousthicknesses. In one aspect, for example, the passivation region has athickness of from about 100 nm to about 1 micron. In another aspect, thepassivation region has a thickness of from about 5 nm to about 100 nm.In yet another aspect, the passivation region has a thickness of fromabout 20 nm to about 50 nm. It should be noted that, in cases where thetextured region is a portion of the passivation region (e.g. adielectric layer) that has been textured, the thickness of thepassivation material would be increased to account for the texturing.Thus the thickness ranges for the passivation region provided here wouldbe measured as the thickness of the passivation region not including thetextured portion.

The devices according to aspects of the present disclosure canadditionally include one or more reflecting regions. In one aspect, asis shown in FIG. 6, a BSI photosensitive imager device 60 can include areflecting region 62 coupled to the textured region 38. It should benoted that all reference numbers in FIG. 6 that have been reused fromprevious figures and will be reused in subsequent figures denote thesame or similar materials and/or structures whether or not furtherdescription is provided. The reflecting region can be deposited over theentire textured region or only over a portion of the textured region. Insome aspects, the reflecting region can be deposited over a larger areaof the device than the textured region. The reflecting region can bepositioned to reflect electromagnetic radiation passing through thetexture region back through the textured region. In other words, aselectromagnetic radiation passes into the semiconductor substrate 32, aportion that is not absorbed contacts the textured region. Of thatportion that contacts the textured region, a smaller portion may passthough the textured region to strike the reflecting region and bereflected back through the textured region toward the semiconductorsubstrate.

A variety of reflective materials can be utilized in constructing thereflecting region, and any such material capable of incorporation into aphotosensitive device is considered to be within the present scope.Non-limiting examples of such materials include a Bragg reflector, ametal reflector, a metal reflector over a dielectric material, atransparent conductive oxide such as zinc oxide, indium oxide, or tinoxide, and the like, including combinations thereof. Non-limitingexamples of metal reflector materials can include silver, aluminum,gold, platinum, reflective metal nitrides, reflective metal oxides, andthe like, including combinations thereof. In one aspect, as is shown inFIG. 7, a BSI photosensitive imager device 70 can include a dielectriclayer 72 positioned between the reflecting region 62 and the texturedregion 38. It should be noted that all reference numbers in FIG. 7 thathave been reused from previous figures and will be reused in subsequentfigures denote the same or similar materials and/or structures whetheror not further description is provided. In one specific aspect, thedielectric layer can include an oxide layer and the reflecting regioncan include a metal layer. The surface of the metal layer on an oxideacts as a mirror-like reflector for the incident electromagneticradiation from the backside. It should be noted that the reflectiveregion is not biased with a voltage.

In another aspect, the textured region 38 can include a hemisphericalgrained polysilicon or coarse grained polysilicon material and thereflective region 62 can include a metal layer. The hemisphericalgrained or coarse grained silicon can act as a diffusive scattering sitefor the incident optical radiation and the dielectric layer 72 and thereflective region together can act as a reflector.

In still another aspect, the photosensitive imager can include selectiveepitaxial silicon growth for generating the textured region on top ofthe junction formed by the doped regions (e.g. a photodiode) without thepassivation region being present (not shown). An oxide and metalreflector, for example, can be coupled to the textured region. Theepitaxial growth places the textured region away from the top of thejunction, and the rapid etch characteristics of grain boundaries can beused to create texturing.

Additionally, the textured surface of a metal on a roughened oxide canact as a diffusive scattering site for the incident electromagneticradiation and also as a mirror-like reflector. Other aspects can utilizeporous materials for the texturing. Porous polysilicon, for example, canbe oxidized or oxide deposited and a reflective region such as a metalreflector can be associated therewith to provide a scattering andreflecting surface. In another aspect, aluminum can be subjected toanodic oxidation to provide porous aluminum oxide, a high dielectricconstant insulator. This insulator can be coated with aluminum or othermetals to provide a scattering and reflecting surface.

In one specific aspect, a reflective region can include a transparentconductive oxide, an oxide, and a metal layer. The transparent oxide canbe textured and a metal reflector deposited thereupon. The texturedsurface of the metal on a roughened transparent conductive oxide can actas a diffusive scattering site for the incident electromagneticradiation.

In another specific aspect, a Bragg reflector can be utilized as areflective region. A Bragg reflector is a structure formed from multiplelayers of alternating materials with varying refractive indexes, or by aperiodic variation of some characteristic (e.g. height) of a dielectricwaveguide, resulting in periodic variation in the effective refractiveindex in the guide. Each layer boundary causes a partial reflection ofan optical wave. For waves whose wavelength is close to four times theoptical thickness of the layers, the many reflections combine withconstructive interference, and the layers act as a high-qualityreflector. Thus the coherent super-positioning of reflected andtransmitted light from multiple interfaces in the structure interfere soas to provide the desired reflective, transmissive, and absorptivebehavior. In one aspect, the Bragg reflector layers can be alternatinglayers of silicon dioxide and silicon. Because of the high refractiveindex difference between silicon and silicon dioxide, and the thicknessof these layers, this structure can be fairly low loss even in regionswhere bulk silicon absorbs appreciably. Additionally, because of thelarge refractive index difference, the optical thickness of the entirelayer set can be thinner, resulting in a broader-band behavior and fewerfabrications steps.

Additional scattering can be provided by positioning a textured forwardscattering layer on the side of the pixel opposing the doped photodioderegions or on the illuminated side. These forward scattering layers canbe, without limitation, textured oxides or polysilicon without areflector. These layers can be spaced away from the back side surface ofthe pixel and would provide scattering of the light in addition to thatprovided by layers on the front side of the pixel adjacent to thephotodiode and transistor doped regions.

In one aspect, as is shown in FIG. 8, a BSI photosensitive imager device80 can include a lens 82 coupled to the semiconductor substrate 32 on aside facing incident electromagnetic radiation. It should be noted thatall reference numbers in FIG. 8 that have been reused from previousfigures denote the same or similar materials and/or structures whetheror not further description is provided. Thus the lens can focus theelectromagnetic radiation more effectively into the semiconductorsubstrate. In the case of a BSI photosensitive device, the lens isdisposed on the backside of the device. Additionally, an anti-reflectivecoating 84 can be associated with the device between the semiconductorsubstrate and the lens. It should be noted that the present scope alsoincludes aspects having a lens without an anti-reflecting coating, andaspects having an anti-reflecting coating associated with thesemiconductor substrate without a lens. Additionally, a color filter(not shown) can be optically coupled to the lens to allow specificwavelengths filtering of the electromagnetic radiation. Incidentelectromagnetic radiation passing through the color filter prior tocontacting the semiconductor substrate can be filtered according to thecharacteristics of the filter.

In another aspect, as is shown in FIG. 9, a BSI photosensitive imagerdevice 90 can also include at least one isolation feature 92 associatedwith the semiconductor substrate 32. It should be noted that allreference numbers in FIG. 9 that have been reused from previous figuresdenote the same or similar materials and/or structures whether or notfurther description is provided. Isolation features can maintain pixelto pixel uniformity when multiple pixels are used in association byreducing optical and electrical crosstalk there between. The isolationfeature can be shallow or deep, depending on the desired design. Theisolation features can be generated using various materials including,without limitation, dielectric materials, reflective materials,conductive materials, light diffusing features, and the like.Additionally, in some aspects the isolation feature can be a void in thesemiconductor substrate. In one aspect, isolation features can also beconfigured to reflect incident electromagnetic radiation until it isabsorbed, thereby increase the effective absorption length of thedevice. Furthermore, the devices according to aspects of the presentdisclosure can also independently include one or more vias, passivationlayers, and the like (not shown).

FIG. 10 shows a photosensitive imager 100 comprising two photosensitivepixels 102. Each photosensitive pixel includes a boundary region 104that can include circuitry and a textured region 106. Eachphotosensitive pixel can include at least one transistor 108 or otherelectrical transfer element. Additional read out and circuitry elements109 can be utilized and shared by both photosensitive pixels.

In other aspects of the present disclosure, various methods of makingphotosensitive diodes, pixels, and imagers, are contemplated. In oneaspect, as is shown in FIG. 11, a method of making abackside-illuminated photosensitive imager device can include forming atleast one junction at a surface of a semiconductor substrate 112,forming a passivation region over the at least one junction 114, andforming a textured region over the passivation region 116. Thepassivation region isolates the at least one junction from the texturedregion, and the semiconductor substrate and the textured region arepositioned such that incoming electromagnetic radiation passes throughthe semiconductor substrate before contacting the textured region. Themethod also includes coupling an electrical transfer element to thesemiconductor substrate 118 such that the electrical transfer element isoperable to transfer an electrical signal from the at least onejunction. In one aspect, multiple pixels can be associated together toform an imager. A passivation layer can also be disposed on the backsideof the photosensitive imager device to protect and/or reduce the darkcurrent of the device.

In another aspect of the present disclosure, a method for making aphotosensitive diode is provided. Such a method can include forming atleast one cathode and at least one anode on a surface of a semiconductorsubstrate, depositing a passivation region on the semiconductorsubstrate over the cathode and the anode, and forming a textured regionover the passivation layer. An electrical transfer element can bedeposited on the semiconductor substrate and can be electrically coupledto at least one of the anode and cathode to form a photosensitive pixel.In some cases, the electrical transfer element can be electricallyisolated from the semiconductor substrate. In another aspect, thesemiconductor substrate can be thinned to improve the response rateand/or speed of the device.

Of course, it is to be understood that the above-described arrangementsare only illustrative of the application of the principles of thepresent disclosure. Numerous modifications and alternative arrangementsmay be devised by those skilled in the art without departing from thespirit and scope of the present disclosure and the appended claims areintended to cover such modifications and arrangements. Thus, while thepresent disclosure has been described above with particularity anddetail in connection with what is presently deemed to be the mostpractical embodiments of the disclosure, it will be apparent to those ofordinary skill in the art that numerous modifications, including, butnot limited to, variations in size, materials, shape, form, function andmanner of operation, assembly and use may be made without departing fromthe principles and concepts set forth herein.

What is claimed is:
 1. A photosensitive imager device, comprising: aplurality of semiconductor devices including semiconductor substrateshaving a light incident side and multiple doped regions forming at leastone junction; a textured region coupled to the light incident side ofthe semiconductor substrate and positioned to interact withelectromagnetic radiation; and at least one isolation feature operableto isolate the plurality of semiconductor devices from each other. 2.The device of claim 1, wherein the at least one isolation featureoperable to electrically isolate the plurality of semiconductor devicesfrom each other.
 3. The device of claim 1, wherein the at least oneisolation feature operable to optically isolate the plurality ofsemiconductor devices from each other.
 4. The device of claim 1, whereinthe at least one isolation feature is a deep trench isolation feature.5. The device of claim 1, wherein the at least one isolation feature isa shallow trench isolation feature.
 6. The device of claim 1, whereinthe at least one isolation feature includes a material selected from thegroup consisting of, metals, oxides, polymers, or combinations thereof.7. The device of claim 1, wherein the at least one isolation featureincludes a reflecting material.
 8. The device of claim 1, furthercomprising a second textured region coupled to the semiconductorsubstrate opposite the light incident side.
 9. The device of claim 1,further comprising a reflective layer coupled to the semiconductorsubstrate and positioned to interact with electromagnetic radiation. 10.The device of claim 9, wherein the reflective layer includes a materialselected from the group consisting of metal, oxide, or combinationsthereof.
 11. The device of claim 9, wherein the reflective layer is aBragg reflector.
 12. The device of claim 1, wherein the semiconductorsubstrates are epitaxially grown.
 13. The device of claim 1, furthercomprising at least on electrical transfer element functionally coupledto the plurality of semiconductor devices.
 14. The device of claim 1,wherein the semiconductor substrates are comprised of silicon.
 15. Thedevice of claim 1, wherein the textured region is formed by a techniqueselected from the group consisting of lasing, chemical etching,anisotropic etching, isotropic etching, nanoimprinting, additionalmaterial deposition, and combinations thereof.
 16. The device of claim1, wherein the photosensitive imager device is a backside illuminatedimager device.
 17. The device of claim 1, wherein the photosensitiveimager device is a front side illuminated imager device.